No Entity Manager with actual transaction available for current thread - cannot reliably process 'persist' call - spring

Question

From service layer which is annotated as Transactional; another service of an external jar is called which is interacting with DB using entity manager(autowired) .
But I am getting this error that "No entity manager with actual transaction available for current thread".
Later I tried to create entity manager manually via EntityManager.getEntityManagerFactory().createEntityManager() which creates the entity manager and then I needed to manually start the transaction also.
My query is : 1. why transaction is not getting propagated to service of external jar.
2. Why autowired EntityManager in external jar is giving error of "No entity manager with actual transaction available for current thread".

Answer 1

General configuration which I provided is:
Appconfig class
#Configuration
#EnableWebMvc
#ComponentScan(basePackages = { "base.package.*" })
#PropertySource("classpath:application-development.properties")
public class AppConfig implements WebMvcConfigurer{}
JNDI config class:
#Configuration
#EnableTransactionManagement
#PropertySource({ "classpath:persistence-jndi.properties" })
#EnableJpaRepositories(basePackages = "base.package.*", entityManagerFactoryRef = "em", transactionManagerRef = "tm")
public class PersistenceConfig {
#Autowired
private Environment env;
#Bean
#Primary
public LocalContainerEntityManagerFactoryBean em() {
final LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
em.setDataSource(ds());
em.setPackagesToScan(new String[] {"base.package"});
final HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
em.setJpaVendorAdapter(vendorAdapter);
final HashMap<String, Object> properties = new HashMap<String, Object>();
properties.put("hibernate.hbm2ddl.auto", env.getProperty("hibernate.hbm2ddl.auto"));
properties.put("hibernate.dialect", env.getProperty("hibernate.dialect"));
em.setJpaPropertyMap(properties);
return em;
}
#Bean
public DataSource ds() {
try {
return (DataSource) new JndiTemplate().lookup(env.getProperty("jdbc.url"));
} catch (NamingException e) {
return null;
}
}
#Bean
#Primary
public PlatformTransactionManager tm() {
final JpaTransactionManager transactionManager = new JpaTransactionManager();
transactionManager.setEntityManagerFactory(em().getObject());
return transactionManager;
}
}
After this setup, I gave #transactional spring annotation at my application's service class which calls the StorageImpl class defined in external jar which is like:
#Repository
public class StorageImpl implements StorageInterface {
#PersistenceContext(unitName = "default")
private EntityManager em;
public saveData(){
em.persist(somedata); // here it is giving error like No Entity Manager with actual transaction available for current thread - cannot reliably process 'persist' call
}
}